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(#) Unnecessary parent layout

!!! WARNING: Unnecessary parent layout
   This is a warning.

Id
:   `UselessParent`
Summary
:   Unnecessary parent layout
Severity
:   Warning
Category
:   Performance
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   Initial
Affects
:   Resource files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/UselessViewDetector.java)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UselessViewDetectorTest.kt)
Copyright Year
:   2011

A layout with children that has no siblings, is not a scrollview or a
root layout, and does not have a background, can be removed and have its
children moved directly into the parent for a flatter and more efficient
layout hierarchy.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
res/layout/useless.xml:13:Warning: This LinearLayout layout or its
FrameLayout parent is unnecessary [UselessParent]
    &lt;LinearLayout
     ------------
res/layout/useless.xml:47:Warning: This LinearLayout layout or its
FrameLayout parent is unnecessary; transfer the background attribute to
the other view [UselessParent]
    &lt;LinearLayout
     ------------
res/layout/useless.xml:65:Warning: This LinearLayout layout or its
FrameLayout parent is unnecessary; transfer the background attribute to
the other view [UselessParent]
    &lt;LinearLayout
     ------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`res/layout/useless.xml`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~xml linenumbers

&lt;merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" &gt;

    &lt;!-- Neither parent nor child define background: delete is okay --&gt;

    &lt;FrameLayout
        android:id="@+id/LinearLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent" &gt;

        &lt;LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent" &gt;

            &lt;TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" /&gt;
        &lt;/LinearLayout&gt;
    &lt;/FrameLayout&gt;

    &lt;!-- Both define background: cannot be deleted --&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/bg" &gt;

        &lt;LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@drawable/bg" &gt;

            &lt;TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" /&gt;
        &lt;/LinearLayout&gt;
    &lt;/FrameLayout&gt;

    &lt;!-- Only child defines background: delete is okay --&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" &gt;

        &lt;LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:background="@drawable/bg" &gt;

            &lt;TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" /&gt;
        &lt;/LinearLayout&gt;
    &lt;/FrameLayout&gt;

    &lt;!-- Only parent defines background: delete is okay --&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/bg" &gt;

        &lt;LinearLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent" &gt;

            &lt;TextView
                android:layout_width="wrap_content"
                android:layout_height="wrap_content" /&gt;
        &lt;/LinearLayout&gt;
    &lt;/FrameLayout&gt;

    &lt;!-- Leaf cannot be deleted because it has a background --&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/bg" &gt;
    &lt;/FrameLayout&gt;

    &lt;!-- Useless leaf --&gt;

    &lt;FrameLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent" &gt;
    &lt;/FrameLayout&gt;
&lt;/merge&gt;
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/UselessViewDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `UselessViewDetector.testUseless`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Adding the suppression attribute `tools:ignore="UselessParent"` on
  the problematic XML element (or one of its enclosing elements). You
  may also need to add the following namespace declaration on the root
  element in the XML file if it's not already there:
  `xmlns:tools="http://schemas.android.com/tools"`.

  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;AbsoluteLayout xmlns:tools="http://schemas.android.com/tools"
      tools:ignore="UselessParent" ...&gt;
    ...
  &lt;/AbsoluteLayout&gt;
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="UselessParent" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'UselessParent'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore UselessParent ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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